Given an array of integers nums
and an integer k
. A continuous subarray is called nice if there are k
odd numbers on it.
Return the number of nice sub-arrays.
Example 1:
Input: nums = [1,1,2,1,1], k = 3
Output: 2
Explanation: The only sub-arrays with 3 odd numbers are [1,1,2,1] and [1,2,1,1].
Example 2:
Input: nums = [2,4,6], k = 1
Output: 0
Explanation: There is no odd numbers in the array.
Example 3:
Input: nums = [2,2,2,1,2,2,1,2,2,2], k = 2
Output: 16
Constraints:
-
1 <= nums.length <= 50000
-
1 <= nums[i] <= 10^5
-
1 <= k <= nums.length
SOLUTION:
class Solution:
def numberOfSubarrays(self, nums: List[int], k: int) -> int:
n = len(nums)
ctr = 0
odd = 0
prefix = [0] * (n + 1)
for i in range(n):
prefix[odd] += 1
if nums[i] & 1:
odd += 1
if odd >= k:
ctr += prefix[odd - k]
return ctr
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